TIL - Docker secrets and BuildKit

Today I was initially struggling to build a container image using Docker BuildKit, via : -

DOCKER_BUILDKIT=1 docker build

and was somewhat confused by a reference to to : -

cat /run/secrets/SECRET.TXT

in the Dockerfile, given that I didn't have a file called /run/secrets/SECRET.TXT.

Thankfully, this article came to my rescue: -

Don’t leak your Docker image’s build secrets

where I use a new ( to me ) Docker CLI argument - --secret - to specify the ID of, and path, to the file on my local file-system that contains the secret.

Easy when you know ?